Fiber bed mist eliminators have found wide application in the removal of suspensions of liquid and soluble and insoluble solid particles (i.e., aerosols) from gas streams emitted from a variety of industrial processes. For convenience, the term “aerosols” as used herein and in the claims refers collectively to gaseous suspensions of liquid and/or solid particles that may be soluble or insoluble in the entrained liquid. Some of the more frequent applications include removal of acid mists, such as sulfuric acid mists, in acid manufacturing, removal of plasticizer mists in the manufacture of polyvinyl chloride floor or wall coverings and removal of water soluble solid aerosols from the emissions of ammonium nitrate prill towers. In these various applications, fiber bed mist eliminators may achieve separation efficiencies of 99% or greater.
Fiber bed mist eliminators typically comprise one or more substantially vertical cylindrical fiber bed elements installed in a suitable vessel. Conventional fiber bed elements comprise beds of collecting fibers in contact with wire screens or similar support structures. The fiber bed is designed to collect liquid mists and soluble solid particles entrained in the moving gas stream and drain them through the structure of the bed. More particularly, during operation of a fiber bed mist eliminator, a stream of gas containing an aerosol is made to penetrate and pass through the fiber bed of the fiber bed element with a horizontal component of movement. The fibers in the fiber bed capture the aerosol in the gas by the mechanisms of impaction, interception, and/or Brownian diffusion. Captured liquid particles coalesce on the fibers to form droplets of liquid in the fiber bed. The moving gas urges the droplets to move toward the downstream face of the fiber bed as gravity pulls the captured liquid downward.
Liquid and/or soluble solids collected by the fiber bed drain through the fiber bed and/or on the downstream surface thereof to the bottom of the fiber bed. From there, the collected material is drained, as through a liquid drain pipe (sometimes referred to as a “seal leg”) having a lower end received in a suitable seal-leg cup or vessel filled with liquid to prevent the escape of gas through the drain pipe. U.S. Pat. Nos. 4,053,290, 4,086,070, 6,106,592 and 7,416,576 disclose seal-leg drain arrangements of this type.
While the operation of a seal-leg drain has proven to be generally satisfactory, this type of drain has the disadvantage of substantially increasing the overall length of the fiber bed assembly. (Seal legs are often two to three feet long.) Further, the seal-leg cup must be filled prior to operation or after failure of the seal due to a pressure spike during the process. Still further, seal legs threaded into the bottom plate of a mist eliminator can become loose if improperly installed, which can cause failure of the seal and bypass of gas around the collection media. Accordingly, there is a need for a fiber assembly which eliminates these disadvantages.